Slot machines use a pay table to list the number of credits a player can win when two or more identical symbols appear on a pay line. Most slot machines have one pay table, listed on the machine’s face or below the spinning wheels. Some machines also have bonus features. Bonus games are typically tied to a particular theme.

In 1891, Sittman and Pitt invented a gambling machine, which featured five drums and fifty card faces. The idea was to mimic the game of poker. It was popular and soon many bars and casinos had the machines in their establishments. Players would insert a nickel into the machine and then watch as the drums spun in hopes of a winning hand. The early slot machines did not have direct payout mechanisms, so prizes were often dependent upon the establishment.

Most slot machines are controlled by a software system. The software is stored in the EPROM or other memory chip. In order to change the software, a casino must physically swap the slot machine’s software. This process is labor-intensive and time-consuming. Moreover, EPROMs are sealed, so only officials from the Gaming Control Board can change them.

Slot machines can malfunction when the amount displayed on the screen is less than the real value. This often goes unnoticed, but can cause a dispute. For example, in 2010 two Colorado casinos reported that their jackpots were incorrect. The Colorado Gaming Commission investigated the machines and found that the jackpot was significantly smaller than what was reported on the screen.